A wide variety of accessories have been developed for users of firearms, to facilitate target visualization and improve targeting accuracy. Among these are laser sighting devices configured to generate a coherent energy beam parallel or nearly parallel to the extension of a gun barrel, with the precise alignment depending largely on the distance to the target and windage. When activated, the coherent energy beam forms a spot of light on the target, to indicate the expected point of impact of the firearm projectile. These devices can enhance the experience of any firearm user, and have considerable importance in certain law enforcement and military operations.
Typical laser sighting devices employ visible red or infrared laser frequencies, as energy at the desired frequency can be generated directly, e.g. with a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal. More recently, it has been discovered that visible light in the “green” range, e.g. having a wavelength in the 490-570 nanometer range, has much higher visibility than visible red laser energy. The more visible beam, while enhancing utility of a sighting device in general, is particularly effective for daytime use.
A difficulty that has limited the use of green laser energy in sighting devices is the need for additional components not required by visible red and infrared lasers. To generate coherent energy in the green region of the spectrum, an Nd:YAG crystal is used to generate energy at a wavelength outside the visible spectrum, e.g. 1064 nm, that is then provided to a frequency doubler, e.g. a potassium titanium oxide phosphate (KTP) or lithium triborate (LBO) crystal to generate the desired wavelength, in this case 532 nm. The additional components require a larger laser drive circuit, typically a printed circuit board, and a larger power supply to meet a higher power requirement. The resulting sighting device is larger and difficult to use with handguns, either because the handgun barrel is not long enough to accommodate the device, or because the device protrudes ahead of the barrel an excessive amount. In accessory devices incorporating green laser sighting and white light (multichromatic energy) illumination, this difficulty is magnified.
Another problem encountered with the green laser is the higher power requirement and the accompanying reduction in useful life of the power source, typically one or more batteries. A larger battery of course contributes to the size of the device; all the more so in devices that combine laser and multichromatic illumination as they typically employ separate voltage level power sources for the separate light sources.
While sighting devices and other accessories can be mounted to firearms in a variety of ways, one approach gaining increasing acceptance involves forming longitudinally extending rails on opposite sides below the barrel of a handgun ahead of the trigger guard, for example as shown in U.S. Pat. No. 6,185,854 (Solinsky et al.). The accessory or auxiliary device is provided with opposed projections, each slidable relative to one of the rails to guide the accessory for longitudinal travel relative to the barrel. The accessory also carries a transverse spring loaded bar that fits into a transverse groove formed in the barrel to secure the accessory against longitudinal travel. While this approach has proven useful for attaching a variety of accessories including laser sights and illumination devices, problems are encountered due to the differences in locations for the transverse grooves among different brands of firearms.